The present invention relates to railroad equipment for “maintenance of way” operations and, in particular, to a system and equipment for automated tie plugging operations and for automated detection of features on a railroad track.
Railroad track generally consists of two parallel rails that are supported on a series of wooden sleepers or cross-ties positioned perpendicular to the rails. The cross-ties are commonly laid on a crushed stone ballast which is packed between and below the cross-ties to hold the track in place. The rails are secured to the tops of the cross-ties by tie plates, which provide a secure housing for the rails and distribute the load over a larger surface of the cross-ties. The tie plates typically comprise a cast or forged steel plate with a substantially flat bottom surface and an upper surface with a pair of parallel ribs that define a cradle area or rail seat for receiving the rail. A plurality of spike holes are formed in the tie plate, on either side of the rail seat. The rails are commonly secured to the tie plates and cross-ties by spikes with offset heads that are driven through the spike holes of the tie-plates and into the wooden cross-ties to clamp the rails to the tie plates.
Over time and with exposure to the elements, cross-ties may become worn or deteriorate to the point where the spikes are only weakly held in the tie and are no longer capable of effectively securing the tie plate and rail to the cross-tie. These worn cross-ties are referred to as “spike killed” ties.
For example, rail traffic exerts repeated lateral and longitudinal forces that can cause the spike holes in the cross-ties to elongate or widen to the point where the rail and tie plate may shift laterally or lift from the cross-tie. The repeated axle loads can also cause “crushed rail seat”, where the wood fibers beneath the tie plate break down to the point where the cross-tie can no longer hold the spike. Seasonal wet/dry and freeze/thaw cycles can cause the wooden cross-tie to develop splits, which progress and widen over time until the cross-tie can no longer hold the spikes. Fungal decay can also break down exposed wood fibers to the point where the cross-tie can no longer hold the spike. In addition, cross-ties can become broken, damaged or burned during the course of service, which may contribute to spike kill.
Spike killed cross-ties are commonly repaired by inserting a wooden plug into the spike hole of the damaged cross-tie, or by filling the spike hole with a resin or other polymeric composition. Such chemical tie plugging compounds include foamed epoxies, polyurethanes and polyureas, as are known in the art.
A variety of equipment has been developed for tie plugging operations, including handheld manual and automated applicators for dispensing tie plugging compounds to fill spike holes in cross-ties. The applicators may also be mounted on railroad equipment that travels on one or both of the rails, where the operator either rides on or walks behind the equipment. Self-propelled, ride-on tie plugging equipment is known in the art, which may be configured with multiple applicators and allow multiple operators to work while seated. These ride-on tie pluggers may also be combined with spike pulling equipment for hydraulic extraction of railroad spikes, to allow coordinated railway repair and maintenance operations. An example of ride-on tie plugging equipment that is commercially available is the Encore RGP Ride-On Rail Gang Plugger (Encore Rail Systems, Inc.—Broomfield, Colo.).
Conventional ride-on tie plugging equipment eliminates much of the manual labor of carrying and dispensing the tie plugging compound. However, the operator is still required to locate and accurately position the applicator over each spike hole to be filled in the cross-ties, which can be a time consuming process. In addition, the repetitive nature of the work may lead to operator fatigue and errors. Thus, it would be desirable to provide tie plugging equipment that automates the process of locating and positioning the applicator over the spike holes in the cross-ties.